Two-way wireless communication systems (WCS) that support inbound calling from the public switched telephone network (PSTN) are well known to those skilled in the art. Examples of such systems include cellular telephone systems and trunked radio systems. In addition to using the PSTN for the transport of calls to and from the WCS, these conventional systems require dedicated, complex centralized switching systems having special controllers for routing the calls. The switching systems are coupled to each of a small plurality of radio transmission sites comprising the fixed part of the WCS.
Simpler, less expensive two-way WCSs have recently become available. An example is the Motorola S35XGB1602AP telepoint base station manufactured by Motorola, Inc. of Schaumburg, Ill. That system comprises a plurality of fixed communication units (FCUs) at a plurality of locations called "telepoints." Each telepoint usually has from two to six FCUs, each FCU being coupled to the PSTN by a telephone line. Each telepoint also comprises at least one location controller (LC) for controlling and coordinating the FCUs at the telepoint.
The FCUs are low power radio transceivers having a maximum communicating range of about 150 meters. A typical large city requires thousands of telepoints for good coverage, but the price of telepoint equipment is low enough to justify the quantity. Additionally, the low power allows frequent reuse of a relatively small amount of radio spectrum to provide a relatively large amount of communication capacity. Thus, unlike cellular and trunked radio systems that use higher power, the telepoint systems can serve large numbers of users in densely populated metropolitan areas.
To use the telepoint for communication a user must be within range and must possess a compatible portable communication unit (PCU). An example is the Motorola S35XCD1000AA personal telephone manufactured by Motorola, Inc. of Schaumburg, Ill. This PCU is a highly portable unit that is more easily transported in one's pocket or purse than conventional cellular PCUs. Because of the low power requirements of the telepoint compatible PCU, it also exhibits a much greater battery life than conventional cellular PCUs.
Unfortunately, conventional telepoint systems do not provide incoming call capability. That is, a telepoint user may originate a call to any destination reachable by the worldwide PSTN, but may not receive any calls. A partial solution to this limitation is for a user to subscribe to a radio paging service and carry a radio pager having a numeric or alphanumeric display in addition to carrying the telepoint PCU. That way, the user can be paged when someone wants to communicate and can subsequently return the call to the number displayed on the pager. For greater convenience there are telepoint compatible PCUs having built-in radio pagers now available. Still, the inability of telepoint users to directly receive incoming calls is viewed by many users as an undesirable limitation.
While it perhaps would be technically possible to use the centralized switching system approach described earlier for routing inbound calls, the large number of telepoints makes this approach economically impractical. Such an approach typically would require thousands of dedicated telephone circuits between the switching system and the telepoint FCUs. A telepoint system is not like a cellular system, which has a far smaller number of radio transmission sites to be interconnected.
Thus what is needed is a way of directly routing inbound calls to telepoint PCUs without requiring a radio paging system including radio pagers, without requiring any additional dedicated switching equipment, and without requiring numerous additional dedicated telephone circuits.